JPS59189833A - X-ray ct apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to an X#CT device (2).

[Technical background of the invention and its problems]

Conventionally, both the R-R type X-ray CT device and the S-R type X-ray CT device (= fan beam (source fan beam or detector fan beam)) Configuration is being done.

However, since the S-R type X-ray CT apparatus originally processes a huge amount of data, the image reconstruction time is extremely long. In addition, since the R-R type X-ray CT device uses continuous X-rays to achieve high-speed scanning and high resolution,
Again, the amount of data to be processed becomes enormous, and as a result, the image reconstruction time becomes extremely long.

On the other hand, in order to shorten the image reconstruction time, for example, with fan beam C: all the obtained data is used for image reconstruction (
Without using two sides (two, for example every second fan beam (:
There is also an X-ray CT apparatus that reconstructs images using only the data obtained from the data, but such X-ray CT apparatuses can only obtain images with significant deterioration in image quality. The purpose of this design is to reduce the amount of data and shorten the image reconstruction processing time, and also to provide an X-ray CT device that minimizes the decrease in spatial resolution and increase in image noise. shall be.

[Summary of the invention]

To achieve the above object, the present invention provides an X-ray tube that emits an X-ray fan beam while rotating around a subject; X-ray CT that has at least a plurality of X-ray detectors capable of detecting fan beams and an image reconstruction device that reconstructs a tomographic image of a subject based on data output from the X-ray detectors.
In the device, data output from the X-ray detector ≦ 2, and among 6 or more sets of adjacent fan data, fan data in the middle part is weighted more heavily than fan data excluding the middle part, and weighted averaging processing is performed. The present invention is characterized in that it includes data bundling processing means for performing weighted averaging processing, and reconstructs a tomographic image using data obtained through weighted averaging processing.

[Embodiments of the invention]

Next, two embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an RR type X-ray CT apparatus which is an embodiment of the present invention, FIG. 2 is a block diagram showing the functions of the computer shown in FIG. 1, and FIG. 6 is a block diagram showing the functions of the computer shown in FIG. 1. FIG. 2 is a flow diagram showing a processing procedure performed by a computer.

As shown in FIG. 1, R-R, which is an embodiment of this invention,
The type X-ray CT device consists of a plurality of X-ray detectors 1 arranged on a circular arc, and the X-ray detector 1 (the two rotate on a circumferential orbit while facing each other, and are located at the center of the circumferential orbit). A gantry 5 equipped with an X-ray tube 4 that irradiates an X-ray fan beam 6 in two directions and the X-ray detector 1 collects data output from the X-ray detector 1, and determines the X-ray irradiation position. A computer 7 having means for realizing the function of the X-ray fan beam C2, which is the key to the fan;
A storage means such as a magnetic disk 8 for writing and reading various data, a console 9 for outputting a command signal for instructing the operation of the computer 7C, and a convolution of the corrected fan data transferred through the computer 7. An image reconstruction device 1.0 that performs image reconstruction processing according to the back projection method≦2, and an image display device 1 that displays a tomographic image reconstructed by the image reconstruction device 10.
1, a high voltage generator 12 that applies a high voltage to the X-ray tube 4 at a predetermined timing in order to irradiate the X-ray fan beam 6 from the X-ray tube 4, the data acquisition device 6, and the high voltage The system controller 16 is configured to include a system controller 16 that controls the operation timing of the generator 12.

The transfer means 7C is comprised of a management means 'ZB' and a transfer means 7C.

The writing/indulging means 7A is the data collecting device #6.
The source fan data outputted from the data bundling processing means 7B and the corrected fan data (described later) outputted from the data bundling processing means 7B are written to the magnetic disk 8 (2), and the written corrected fan data is transferred to the magnetic disk 8 (2).
It also performs control to read the source fan data written on the magnetic disk 8f2 to the data bundling processing means 7BC2.

The data bundling processing means 7B includes the writing/reading means 7
The source fan data written on the magnetic disk 8C2 through A is read out sequentially again through the writing/reading means 7A, and six consecutive sets of source fan data P are read out again through the writing/reading means 7A.
(3mΔF, nΔθ).

P((>+n+1)Δ1, nΔθ), P((3m+
t)ΔF',.

nΔθ)(two, intermediate source fan data P((3
m+i)ΔF, nΔθ) (two pair weighting, and previous and subsequent source fan data P(3mΔW, nΔθ),
m'+2)ΔF, nΔθ) (The ratio of the two weightings is set to 2:1, and the weighted average is calculated as shown in the first equation to calculate the corrected fan data P'((3mH)ΔF, nΔθ) is output.

F'((3m+x)△W, n△θ) = 4(p(3m△y, n△θ)+2P((3m+1)△
W.

n△θ)+P ((3m+2)△?/', n△θ month...
・・・・・・・・・(1) However, as shown in FIG. f 3m, f 3m+1, f 3m+2 (
m is the central angle between 0 and the rotation center 0 of the X-ray tube 4, and Δθ is the angular pitch of each X-ray beam forming the fan beam. Further, n is an integer indicating the number of each X-ray beam making up the fan beam.

The data bundling processing means 7B performs data bundling processing from m=0 to m=H -7-1 according to the first equation for all the source fan data ζ.

Furthermore, the data bundling processing means 7B performs weighted averaging (
The corrected fan data y obtained in step 2 is transferred to the magnetic disk 8 via the writing/reading means 7A, and the fan data used for weighted averaging is not outputted (discarded).

The transfer means 7C is configured to sequentially read out the corrected fan data written on the magnetic disk 8 via the write/read means 7A and transfer the corrected fan data to the image reconstruction device 10C. In addition, in this invention (2), the transfer means 7C is omitted, and the corrected fan data written on the magnetic disk 8 is transferred to the image reconstruction device 10 (2) immediately from the writing/reading means 7A (2). You may.

Next, the operation of the above configuration (C2 will be explained together with the flow shown in Figure 4).

As shown in FIGS. 1 and 5 (2. While the X-ray tube 4 rotates on its circumferential orbit, each X-ray irradiation position f3m is set.

The X-ray fan beam 3 is irradiated toward the subject 2 at f 3m+1 and f 3m+2. X transmitted through object 2
The ray fan beam 6 is detected by the X-ray detector 1, and the data output from the X-ray detector 1 is collected by the data collection device 6. The data collection device "6 has each X-ray irradiation position f3m,
f3m+1. A data group consisting of a plurality of data output from a plurality of X-ray detectors 1 into which the X-ray fan beam 6 irradiated at f3m+2 is incident is collected as a whole and collected as source fan data 2H. /ΔV source fan data are sequentially output from the computer 7C. As shown in FIG. 2, the computer 7 writes the source fan data sequentially sent by the writing/reading means 7A to the magnetic disk 8.
The writing/reading means 7A reads out 211/ΔV source fan data to the data bundling processing means 7Bl2.

The data bundling means 7B includes adjacent source amplifiers nΔθ
), PC(3m+2)ΔV, nΔθ), the corrected “data P′((3rtl+t)ΔF, nΔθ) is calculated according to the first equation.The obtained corrected fan data is written via the writing/reading means 7A. The writing/reading means 7A performs a data bundling process (does not transfer the source fan data used on the second side to the magnetic disk 81 and discards the source fan data. (The written correction fan data is read out from the writing/reading means 7A (-)
The image is transferred to the image reconstruction device 10C by the transfer means 7C. The image reconstruction device 10 reconstructs a tomographic image of the subject using the transferred corrected fan data. The reconstructed tomographic image is displayed on an image display device 11 (2).

As mentioned above, by performing data bundling processing on the computer 7 (obtaining corrected fan data that is X of the number of source fan data from 2, and reconstructing an image from this corrected fan data C2, image reconstruction is performed. Processing time can be significantly shortened. In other words, image reconstruction can be speeded up.

Moreover, when the weighted average bundling process is performed, the C-2 spatial resolution can be improved and image blurring can be reduced, as shown below, compared to the case where a simple arithmetic mean bundling process without weighting is performed.

The interpolated fan data obtained by arithmetic averaging of six sets of source fan data can be expressed by the second equation (2).

P'((3m+t)ΔF, nΔθ)=-F(p(3
mΔF, nΔθ) +P ((3m+1)ΔF, nΔ
θ)+P ((am-)Z )8W, n△θ) )-・
-(21 consecutive 6 X-ray exposure positions wf 3m, f
3m+1, f 3m+2 The distance of the n-th X-ray beam constituting the fan beam irradiated at f 3m+2 is the distance between the center of field O and the X-ray exposure position f 3m (f
m+1, f3m+2) (100 f3m
, Qf3m+1, Of3m+2) from a circle with a diameter of Cn, for example -0. This is worst at the outermost periphery of the field of view, and worst for an X-ray beam passing through the center of the field of view (i.e., nK0). If the field of view radius is R(w), then
The worst value of the line beam distance is RΔV. In this case, the blur of the image reconstructed from the corrected fan data C2 obtained from the second equation C2 is evaluated using the sixth equation C2.

F(f)4(1+2coa(217fRΔF))
...-(sl) In other words, the filter given by the 6th equation is applied (2). In the 3rd equation C2, f is the wall frequency (7tne pair/m), and the cutoff of the filter The frequency fco is expressed by the fourth equation.

fco='cos(--)09. ”14)21
1RΔF z On the other hand, the blur of the image reconstructed from the corrected fan data l2 obtained by the first equation is evaluated as having been filtered by the fifth equation.

F(f)4(1+2cos(2HfRΔF))
(5) The cutoff frequency in the fifth equation is expressed by the sixth equation.

fco = 7r "1 μos (-1) - Song (6) Therefore, the cutoff frequency shown by the 6th equation is 1.5 times the cutoff frequency shown by the 4th equation, and accordingly,
Spatial resolution is improved.

In addition, the bundling process using the weighted average l2 in Example C2 generates noise, but as shown in the following (2),
Second, the extent of this is slight.

Ks is the signal of each source fan beam before bundling.

If Kn is the noise, then the corrected fan beam signal obtained by the arithmetic mean shown in the second equation C2 is TX! 1KB=Ks
Since the noise is 10 KA + KA + KA = ≠, the signal-to-noise ratio is .

On the other hand, the corrected fan beam signal obtained by the first equation is
-'((Ks+2Ks+Ks)==Ks, and if we perform the bundling process using weighted averaging for that noise,
In the case of bundling processing using simple arithmetic averaging, the signal-to-noise ratio is (44)/g = 0.94 times (2), and this level of reduction in the signal-to-noise ratio is sufficient for practical use.

Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above-mentioned embodiment, and can be implemented with appropriate modification within the scope of the gist of the present invention. Needless to say.

In Example C2, the weighted averaging process was performed on three sets of source fan data, but the weighted averaging process may be performed on four or more sets of source fan data. Further, although the weighting during the weighted averaging process is 1':2:1 in the above embodiment, it is not limited to this, and may be appropriately set such as 1:3:1 or 2:6:2. .

In the embodiment described above, six consecutive sets of source fan data are weighted and averaged.
Applying it to a line CT device, the obtained source fan data is rearranged to form detector fan data, and then six consecutive sets of detector fan data are subjected to weighted averaging processing, and the obtained corrected detector fan data (secondary It is also possible to carry out image reconstruction processing.In this case, it goes without saying that the computer 7 must be provided with data rearrangement means for rearranging the source fan data into the detector fan data.

〔Effect of the invention〕

According to this invention C2, the amount of data required for image reconstruction C2 can be reduced to a fraction or less, and thus the calculation time required for image reconstruction processing can be significantly shortened. , it is possible to improve the spatial resolution of the obtained image, and it is also possible to suppress a decrease in the signal-to-noise ratio to a practically negligible level.

[Brief Description of the Drawings] Figure 1 shows an R-R type XfJIC which is an embodiment of the present invention.
FIG. 2 is a block diagram showing the functions of the computer in FIG. FIG. 1 is a flowchart showing the processing procedure based on the computer (C2), and FIG. It is an explanatory diagram for calculating. 1... X-ray detector, 2... Subject, 6... X
ray fan beam, 4... X-ray tube, 7B... data bundling processing means, 10... image reconstruction device.

Claims (1)

[Claims] An X-ray tube that emits an X-ray fan beam while rotating around the subject, an X-ray detector arranged on the circumference or on an arc, and data output from the X-ray detector In an X-ray CT apparatus that has at least an image reconstruction device that reconstructs a tomographic image of a subject based on the image data, an intermediate part of six or more adjacent sets of fan data is output from the X-ray detector and has no data. The present invention is characterized in that it includes a data bundling processing means that performs weighted hilar averaging processing by weighting the fan data in the middle part more than the fan data excluding fan data, and reconstructs a tomographic image using the data obtained by weighted averaging processing. X-ray CT
Device.